GUNTOWN, Mississippi (CNN) -- Federal authorities added the suspect in the kidnapping of four members of a Tennessee family to the FBI's 10 most wanted list Wednesday and added $100,000 to the rewards offered for a break in the case.

Adam Mayes is accused of killing two of the victims, but investigators hope to find the remaining two -- both young girls -- alive, said Aaron Ford, the special agent in charge of the FBI's Memphis office. Ford spoke made the announcement in Guntown, Mississippi, where authorities were searching for Mayes.

"We are moving forward with our investigation to hunt down Adam Mayes and rescue those two little girls," he said. He urged Mayes to leave the girls in a "safe location," such as a police station, church or hospital, "and then peacefully and safely turn yourself in."

The two young sisters, 12-year-old Alexandria and 8-year-old Kyliyah Bain, were the targets of a kidnapping plot that involved the killing of their mother and older sister, a Tennessee court document states. The bodies of the girls' mother, Jo Ann Bain, and elder sister Adrienne were found over the weekend.

The federal reward brings the total amount of money offered for information leading to Mayes' arrest to $175,000, Ford said. Mayes' wife, Teresa Mayes, and his mother, Mary Frances Mayes, are in custody, but Mayes himself continues to evade a small army of 17 law enforcement agencies and hundreds of searchers.

Adam and Teresa Mayes each have been charged with two counts of first-degree murder and two counts of especially aggravated kidnapping. Adam Mayes faces an additional count of making a false report, according to arrest affidavits filed in Tennessee. In an interview with police, Teresa Mayes said her husband intended to take Alexandria and Kyliyah from their home in Hardeman County, near Memphis.

Police said she told them she was in the Bains' garage where Adam Mayes killed Jo Ann and Adrienne Bain.

"Both murders were directly a part of the kidnapping" of the two younger girls, the document alleges. Details about time or cause of death haven't been released.

Adam and Teresa Mayes then transported the bodies to Union County in northern Mississippi, where they were discovered Saturday in a shallow grave behind Adam Mayes' mother's house in Guntown.Teresa Mayes and Adam Mayes' mother, Mary Frances Mayes, were arrested Tuesday in connection with the kidnappings. The mother has been charged with four counts of conspiracy to commit especially aggravated kidnapping.

Teresa Mayes' lawyer, Shana Johnson, said her client is cooperating with police but would not say whether she knows the whereabouts of Adam Mayes or the girls. The Mayes family and the Bain family are connected through Adam Mayes' sister Pamela, who used to be married to Jo Ann's husband, Gary Bain, the lawyer said.

Adam and Teresa Mayes have been married for 11 years and lived in Guntown, she said. Johnson said she has asked for a mental health evaluation of her client.

Bobbi Booth, Teresa Mayes' sister, spoke to CNN's Anderson Cooper on Tuesday about Adam Mayes and his relationship with her sister, who she said has mental health problems.

"I've known Adam for at least 25 years, and he's always been weird and unusual ... but I never dreamed he would do something like this," she said.

She described him as aggressive and not trustworthy. He beat and threatened to kill her sister, said Booth, who pleaded with him to "do the right thing."

"Just let the children go. This has gone on way too far, and we need to figure out what's going on, and it's not fair to the children," she said.

Authorities tried to interview Mayes soon after Gary Bain reported his wife and the girls missing April 27 in Whiteville, a western Tennessee town of 4,600 people. However, Mayes fled, officials said.

He was last seen May 1 in Guntown. Mayes may be using the alias of Christopher Zachery Wylde or Paco Rodrigass, his Facebook profile name, the FBI said Monday. Authorities describe Mayes as a white man with blue eyes and brown hair, 175 pounds and 6-foot-3. He recently cut his hair and may have done the same to the missing girls.

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